Reinforced connection for a electronic circuit members and method for constructing therefor

ABSTRACT

For electronic circuit members including a high density fine pattern electrode and a flexible printed circuit, a reinforced connecting part includes a reinforcing fastener which is a substantially cylindrical section shaped element having edges defining an axial slit clamping the circuit members. The reinforcing fastener is formed of an alloy having both superelastic and shape memory characteristics at a temperature above the Martensite transformation temperature of the alloy. The alloy is brought to a temperature above the Martensite transformation temperature after the slit is opened at a temperature below the Martensite temperature of the alloy and the electronic circuit members are attached via the slit. The circuit members can thus be fastened with a substantially constant force over time due to the superelastic and shape memory characteristics of the alloy.

This application is a continuation-in-part of application Ser. No.111,200, filed on Oct. 22, 1987, now U.S. Pat. No. 4,846,709.

BACKGROUND OF THE INVENTION

The present invention relates to a reinforced connection part ofchemical connectors such as an anisotropic electroconductive membrane,elastomer connector, etc. and a method of construction therefor. Itconcerns, in particular, improvements in reliability in high-temperatureregions during long term use.

Recently, chemical connectors such as anisotropic electroconductivemembranes, elastomer connectors, etc. have been used for the connectionof high-density finepattern electrodes such as a Liquid Crystal Display(LCD), a Light Emitting Diode (LED), an Electroluminescence (EL), etc.to a flexible printed circuit (FPC). For example, when the transparentelectrode (hereinafter abbreviated as ITO membrane electrode-ITO) beingan electrode on the side of an LCD, and a FPC to drive it are joined, amethod of heating under pressure allowing the anisotropicelectroconductive membrane (membrane conducting to the direction ofthickness but not conducting to the direction of width) to lie betweenboth has been adopted for adhesion. But, since the base resin of thiselectroconductive membrane is of hot-melt type, the adhesive forcetended to decrease at a raised temperature. Moreover, in the case of theso called zebra connector, a sheet-like connector made in such a waythat silicone type rubber and electroconductive layer admixed finepowders such as carbon black etc. with said rubber are superposedalternately is pressed to be joined by external force. However, withsimple pressing by said external force, there arise inconveniences suchas the occurrence of poor junctions etc. because of the creep etc. ofmaterials occuring at the time of long-term use. In order to improve onthis, a method of joining both electroconductive portions is carriedout, wherein a heat seal connector, the electroconductive portionconsisting of electroconductive pastes such as carbon, Ag, etc. beingformed in the base film of adhesive layer by a printing method, isallowed to lie between said ITO and FPC and brought into adhesion underheat.

Recently, with the advent of the coloration of LCDs and the requirementfor more distinction of image quality, it has become necessary to makethe clearance between conductors in the ITO portion provided on thescreen of an LCD even smaller. Specifically, the pitch betweenelectrodes to be provided for an ITO membrane electrode has dropped from0.4 mm to a level of 0.3 or 0.2 mm, and the heat seal connector used inthe printing method aforementioned has not been able to correspond tothis any longer. In addition, since the use fields of LCDs haveincreased from so-called disposable consumption type products such aswatches, camera and TVs to long-life, high-reliability and durabilitytype products, for example, terminal input-output devices of workstation and OA instruments and planar display products for cars, forwhich high functionality is required, the connector system used up tothis time as described above has become unsatisfactory.

In such a situation, a method is known wherein not only saidhigh-density fine-pattern electrode and FPC are pressed simply through achemical connector, but also the connection part is fastened tightlywith suitable metal fittings, for example spring materials for thereinforcement. By this method, however, sufficient tightening cannot beobtained, since the size of the connection part, for example thethickness, is extremely small, i.e., around 1.5 mm, the size of a springis restricted so that the deformation quantity of the spring cannot belarge, and the superelasticity of the spring is also a strain of lessthan 1% at most. Moreover, with a large spring, which occupies a largespace, the miniaturization and the thinning of instruments aredifficult, and with a small spring the attachment thereof to theconnection part by deforming it within a limit of elastic deformation isdifficult. Furthermore, the spring materials have such properties thatthe tightening force varies significantly depending on the extent ofstrain, and there is a shortcoming that the tightening is lowereddrastically if creep deformation, etc. are caused in the constituentmaterials of the connection part, for example.

For this reason, in Japanese Unexamined Patent Publication No. Sho61-203698, such a shape memory alloy is disclosed as a metal fitting tohold down and reinforce the connection part. By using this, manyadvantages can be obtained such that the reinforcement of the connectionpart of an electronic circuit becomes extremely easy, the discrepancy ofposition between that at the time of attachment and that at fixationdoes not occur compared with the method to press down physically, theforce of pressing can be controlled by the thickness and the shape ofthe metal fitting and, at the same time, there are no partial floatingsand gaps occuring when using spring materials, so that uniform contactforce can be obtained, and the like. However, the reinforcing metalfitting described in the specification of the foregoing patent has ashape as shown in FIG. 2 (G) and, because of the long legs thereof, thecontact with the connection part of electronic circuit becomes a surfacecontact, resulting in that the nonuniformity of the holding area isinevitable. Moreover, in the reinforcing metal fitting, superelasticityis necessary, but there is no concrete description about this fact inthe specification thereof.

As a result of diligent investigations with respect to these points, theinventors have discovered that the shape and the superelasticity ofreinforcing metal fitting (hereinafter referred to as a fastener)comprising the shape memory alloy affect significantly the reliably athigh-temperatures in use over a long term, leading to the presentinvention.

SUMMARY OF THE INVENTION

The present invention provides a method, wherein the miniaturization andthe thinning of an LCD, etc. are possible and the improvement in thereliability of connection between the ITO and the FPC also becomespossible. Namely, onto said connection of electronic circuit memberscomprising an ITO, a chemical connector and an FPC, or an ITO and FPC,is positioned a reinforcing fastener which comprises a superelasticshape memory alloy and which is machined into a circular shape, ellipticshape, flattened elliptic shape or preferably horseshoe shape in sectionwith a slit in the axial direction The connection part is heldinsertedly in the slit through linear contact by means of the tighteningforce generating through the recovery in shape of said fastener, and atightening force can become a uniform holding force through anadditional superelastic effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example of the reinforced connection part of thechemical connector according to the invention.

FIGS. 2 (A) through (D) respectively show the fasteners of the inventionin horseshoe shape, circular shape, elliptic shape and flattenedelliptic shape in section.

FIG. 2 (E) and (F) show the sectioned shapes of other fasteners whichare shown for reference.

FIG. 2 (G) is the fastener in U shape in section with long legs, whichhas been used conventionally.

FIG. 3 is a diagram showing an outline of the process when attaching thehorseshoe shape fastener in section of the invention.

FIGS. 4 (A) through (D) show a detailed diagram of the process of FIG.3.

FIG. 5 is a diagram showing an another method to assure the openingquantity in the slit of a fastener.

FIG. 6 is a graph showing the stress-strain characteristic of asuperelastic alloy.

FIG. 7 shows the relationship between fit pressure of the fastener and atemperature characteristic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the invention, upon attaching the reinforcing fastener to theconnection part, the shape memory and superelasticity of the alloy areutilized. Thus, a plate of shape memory alloy is rolled up to make acylindrical fastener with a slit in the axial direction thereof. Thecylindrical form may be of circular shape, elliptic shape, flattenedelliptic shape or preferably horseshoe shape in section as shown inFIGS. 2 (A) through 2(D). In this form, both effects of shape memory andsuperelasticity arise at a temperature over the Martensitetransformation temperature (Af point). Then in a state where the elasticforce of the fastener is lowered by cooling to an appropriatetemperature under the Martensite deformation start temperature (Ms), theslit 6 may be opened by means of a slight force, and, by inserting theconnection part thereinto as shown in FIG. 3, the fastener 5 can becovered onto the connection part with ZIF (zero insertion force).Finally, by heating the fastener to above the Af point, or by allowingthe fastener to warm to above the Af point, a force to recover to thememorized shape is generated in the fastener 5 and, by means of thisforce and the force due to superelasticity, the connection becomesfastened tightly and strongly. With the fastener of the invention, theholding pressure becomes uniform over the whole length, since theconnection part is held through linear contact.

One example of the reinforced connection part with the connector of theinvention when using the horseshoe shape fastener in section is shown inFIG. 1. In the diagram, numeral 1 is the liquid crystal, numeral 2 is anITO made on the glass substrate etc., numeral 3 is the chemicalconnector, numeral 4 is the FPC, numeral 5 is the reinforcing fastener,and numeral 7 is the screen.

Further, it is also an important factor for the reinforcing fastener ofthe invention to have superelasticity as well as shape memory. Thesuperelasticity is a property wherein (FIG. 6), even if deformed topoint b, beyond a point which is the usual elastic limit, the strainreturns to 0 via points c and d when the stress is removed (FIG. 6) andthe change of stress versus strain is remarkably smaller in the regionexhibiting the superelasticity, i.e. between c and d, than that in theusual elastic region. Accordingly, if the connection part is fastenedtightly in this region c-d, variations of the tightening force can bekept extremely small despite creep deformation etc. of the materials ofthe connection part. The superelasticity of the material for thefastener of the invention shows an extremely high strain amounting 6 to8%, whereas that of the spring materials made from phosphore bronze etc.is lower than 1%.

In the invention, simple attachment of parts and high reliability aresatisfied by simultaneously utilizing both said shape memory effect andsuperelasticity effect.

As the shape memory alloys with superelasticity usable for the materialsof the reinforcing fastener of the invention, Ni-Ti type alloy (alloymainly composed of intermetallic compounds between Ni and Ti, or alloyssubstituting a part of either or both of Ni and Ti with other elementssuch as Fe, Co, Cu, Cr, etc.) and Cu-Zn type, Cu-Al type, Cu-Zn-Al type,Fe-Si-Mn type, Fe-Ni-Cr type, Fe-NiCo-Ti type and other type alloys canbe mentioned. Thereamong, the use of Ni-Ti type alloy is particularlypreferable. The Af point of the alloy can be established advantageouslybetween 0° and 20° C. in order to recover to the memorized shape in thevicinity of normal temperature.

As the shapes of the fastener, any of horseshoe shape, circular shape,elliptic shape and flattened elliptic shape in section shown in FIG. 2(A) through (D) may be used, but the horseshoe shape in section in (A)is preferable. If the section is circular shape, the bulge when attachedto the connection part is large, resulting in the connector not onlybecoming too thick compared to the depth required for the instrumentsbut also in the danger of causing damage to the connection part by theedges of slit in the course of long term use. Moreover, when forming theplate of alloy, the elongation of the edge tends to occur and, as aresult, warpage is caused to the fastener or the linearity of the slitis damaged to make the tightening force nonuniform in some cases,leading to somewhat poor applicability. The elliptic shape and flattenedelliptic shape in section in (C) and (D) have similar shortcomings to acircular fastener in the above points, except that the bulge whenattached to the connection part becomes small, so that there remainpractical problems. With the fastener in horseshoe shape in section,there is no such fear, and it is preferable because of the capability ofbeing made thin compared to the depth required for the instruments.

FIG. 2 (E) and (F) are sectional shapes of fasteners shown for referenceThere, the fastener in triangular shape in (E), the curvature at thebending portions being steep, has a danger that cracks can occur atthose portions and thus it is not reliable. With the fastener of anapproximately semicircular shape in (F), the holding portion has surfacecontact similarly to a U shape fastener used conventionally and, inaddition, the machining necessary for keeping the unevenness on thecontact surface of the fastener component itself uniform is difficultdue to the hard machinability of shape memory materials. As a result,when so fitted, uniform holding force is hard to obtain.

The fastener of the invention has the slit in the axial direction. Theopening amount of this slit is memorized so that a zero or sufficientlysmall clearance exists relative to the thickness of the connection partto be held. The size of the fastener is 1 to 500 mm in length and about0.3 mm in thickness and, in the case of a horseshoe shape in section, anouter diameter of the bending portion is about 2.3 mm, a width from theback face of bending portion to the tip of flat portion is about 3.9 mmand, in the case of a circular shape, a diameter of 1.5 to 3 mm ispractical, respectively. The tightening force generated with theseshapes is more than zero but not more than 4 kg/cm, though it may bevariable depending on the composition of materials and the temperaturefor heat treatment (refer to FIG. 7).

The fastener formed at over the Af point and given both the effect ofshape memory and superelasticity is then cooled to a temperature belowthe Ms point to open the slit. Using a cooling device 20 as shown, forexample, in FIG. 4 (B) and (C), cooling of the fastener 5 is made toabout -50 ° to -20° C. by placing it insertedly in a concave groove onthe plate 21, and the slit 6 having lower elastic force is opened withan opening adapter 12. When the connection part of electronic circuitmembers is inserted into this opening, then taken out together withfastener 5 and allowed to stand to a normal temperature above the Afpoint of the alloy or heated, the tightening pressure and the force dueto superelasticity are generated together with the shape recovery of thefastener to hold the connection part for reinforcement. For theconnection part, a thin sheet 8, of Teflon, polyethylene terephtalete(PET), or rubbers having elasticity and double face adhesive tape 9 canbe used more conveniently for the attachment of the fastener, as shownin FIG. 4 (A).

For the opening of the slit of the fastener, the following other methodcan be used. After cooling the fastener to a temperature easy fordeformation (below the Ms point), a spacer 13 is allowed to slideaxially while inserting it into the slit 6 as shown in FIG. 5. This isinserted into the concave groove of a cooling device and thereafter thespacer 13 is removed by pulling out. Since the slit 6 is opened by thethickness of spacer 13 at this time, the connection part can be heldinsertedly in the slit by the same procedure as above. According to thismethod, the attachment of fastener 5 becomes extremely easy and novariation occurs in the contacting state of connection part, to permitexcellent reinforcement.

Besides, although the slit portion 6 deforms more or less at the time ofopening with opening adapter 12 or pulling-in of the spacer 13, thememorized shape is recovered due to the shape recovery with an increasein the temperature, if kept as it is.

As evident from the description above, according to the invention, thereliability in a high-temperature region or at the time of use over longterm, which is a shortcoming of the connection through a chemicalconnector, has been enhanced by means of the uniform tightening forcedue to superelasticity to raise the value of products and, at the sametime, a design which is compact and suitable for the miniaturization andthinning, and extremely easy attachment due to shape memorization hasbeen made possible. Therefore, the invention exerts remarkable effectsindustrially.

In the following, the invention will be illustrated in more detail usingexamples, but it is not confined to these.

EXAMPLE 1

Onto a heat-sealed connection part the ITO membrane electrode on theside of an LCD formed on the glass substrate with a thickness of 0.55 mmand FPC stuck copper foils with a thickness of 18 μm onto the polyimidefilm with a thickness of 25 μm at a pitch of 0.2 mm and plated with goldthrough an anisotropic electroconductive membrane with a thickness of200 μm (made by Sony Chemical Co.), a reinforcing fastener in horseshoeshape in section shown in FIG. 2 (A) was covered to form the reinforcedconnection part of the invention shown in FIG. 1.

For the shape memory alloy with superelasticity, Ni-Ti type alloy, theAf point being about 1° C., was used. This was memorized in cylindricalform and in horseshoe shape in section, the size being 70 mm in length,0.3 mm in thickness, 2.3 mm in outer diameter of bending portion and 3.9mm in width from the back face of bending portion to the tip of flatportion, to make the fastener (opening quantity of slit : 0), and, afterwidened the opening quantity of slit to 1.7 mm at -50° C., it wasattached to the connection part.

Using this, high-temperature continuous tests at 80° C. and 100° C. andMIL (STD 202-106) test were conducted to determine the contactresistances at an initial range of test and after 1000 hours, which werecompared with those of a conventional connection part (current appliedon measurement : 0.1 mA). Results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                 Conventional  Connection Part                                                 Connection Part*                                                                            In Example 1                                           ______________________________________                                        High-temperature                                                                         Initial  After      Initial                                                                              After                                   Continuous Test                                                                          Value    1000 hrs.  Value  100 hrs.                                80° C.                                                                            10-20Ω                                                                           >100Ω                                                                              10-20Ω                                                                         <20Ω                                                             Little Change                                  High-temperature                                                                         Initial  Impossible Initial                                                                              10-30Ω                            Continuous Test                                                                          Value    to measure Value                                          100° C.                                                                           10-20Ω        10-20Ω                                   MIL        Initial  After 1    Initial                                                                              After 10                                           Value    cycle      Value  Cycles                                  STD 202-106                                                                              10-20Ω                                                                           >100Ω                                                                              10-20Ω                                                                         10-50Ω                            ______________________________________                                         Note: Average value of N 150 bars × 5 units                             *Hardened with epoxy resin (Heat seal connector)                         

As evident from Table 1, with the connection part used conventionally,the contact resistance after 1000 hours became extremely large at a hightemperature of 80° C. or 100° C. and high resistance resulted after 1cycle also by MIL test. Whereas, with the connection part in accordancewith the invention, the contact resistance hardly changed by the testfor 1000 hours at 80° C. and went no further than extremely slightlyincreasing even by the test for 1000 hours at 100° C. Moreover, theresistance after 10 cycles was not higher than 50 Ω by MIL test, too.

EXAMPLE 2

Onto a heat-sealed connection part, the glass substrate with a thicknessof 1.0 mm, the electrode being printed thereon, and FPC with a thicknessof 100 μm through an anisotropic electroconductive membrane with athickness of 200 μm (made by Sony Chemical Co.), the reinforcingfastener in circular shape in section shown in FIG. 2 (B) was covered toform the reinforced connection part of the invention.

For the shape memory alloy, Ni-Ti type alloy, the Af point being 10° C.,was used. This was allowed to memorize to the shape in cylindrical formwith a diameter of 1.5 mm and an opening quantity of the slit of 1.0 mmto make the fastener and, after widened the opening quantity of the slitto 1.3 mm at -50° C., it was attached to the connection part.

Using this, various tests shown in Table 2 were performed to determinethe contact resistances before and after the test, which were comparedwith a conventional article sealed in the anisotropic electroconductivemembrane with epoxy adhesive. As a result, with the conventionalarticle, remarkable increases in the contact resistances were recognizedunder all conditions shown in Table 2, but, with the article of theinvention, no serious variations were recognized in the contactresistance.

                  TABLE 2                                                         ______________________________________                                        (1)   Heat cycle test 85° C.--35° C., 120 cycles                (2)   High-temperature                                                                              100° C., 1000 hrs.                                     continuous test                                                         (3)   High-temperature,                                                                             60° C., 95% RH, 400 hrs.                               high humidity                                                                 continuous test                                                         (4)   MIL (STD 202-106)                                                                             10 cycles                                               ______________________________________                                         Contact pressure: 2.2 kg/cm at 20° C.                             

EXAMPLE 3

A case when the glass electrode and FPC are fitted directly with thefastener is exemplified.

In the glass substrate with a thickness of 1.1 mm, the electrode beingprinted thereon and, for the electrode, primer plating with nickel andtop plating with gold being given on ITO membrane so as the totalthickness to become 1 to 3 82 m and FPC with a total thickness of 43 μm,(the thickness of Kapton base film is 25 μm, that of copper foil is 18μm and nickel plating and gold plating are given on the foil in total of1 to 5 μm), the width of electrode, the pitch and the number ofelectrodes being 0.5 mm, 1.0 mm and 100, respectively, both electrodeswere positioned to coincide with each other (at this time, if employingmethods such that, with the aid of adhesive layer provided beforehand ona part of FPC side, this is heat-sealed onto the side of glass substratefor temporary fastening, and the like, the positioning of bothelectrodes can be made more easily). Then, the reinforcing fastener inhorseshoe shape in section shown in FIG. 2 (A) was covered and bothelectrode portions were connected with this reinforcing fastener.

Following this, the contact resistance between these both electrodes wasmeasured to determine the initial value, which was 3 to 5 Ω. This samesample was allowed to stand for 1000 hours under an atmosphere at 80° C.for the high-temperature continuous test. Thereafter, the contactresistance between same electrodes was 4 to 7 Ω, showing a slightincrease, but this increase is not problematic at any rate upon use. Onthe other hand, as a conventional comparative example, the connection ofsaid glass electrode to FPC was made in a way that zebra type connectorof sheet-like elastomer described previously was placed on the junctionand was pressed further by external force to connect. According to thisconventional example, initial value was 3 to 5 Ω, but after thetreatment for 500 hours at 60° C., some of 100 electrodes had aresistance of higher than 30 Ω and, when extending the test timefurther, some other electrodes were seen to be worsened to scores ofohms. Based on this fact, it is understood that the example inaccordance with the invention exerts sufficient effect.

EXAMPLE 4

A plate of Ni-Ti alloy (Ni 50%, Ti 50%) with a thickness of 0.3 mm and awidth of 9.5 mm was machined into tube form with a diameter of 3 mm byroll forming and the shape memory treatment was given by fixing it to ajig so that the butt clearance became 0 to make a reinforcing fastenerwith a slit in the axial direction. Then, this fastener was cooled to atemperature easy to be deformed (-30° C.) and a spacer with a width of 7mm, a thickness of 1.5 mm and a length of 220 mm was inserted into theslit portion of the fastener, allowing it to slide in the axialdirection to obtain the fastener for the reinforcement of the connectionpart as shown in FIG. 5.

Then, cooling the fastener being to -30° C., the spacer was pulled outand the connection part was inserted here to be covered by the fastener.The attachment of the fastener was extremely easy, the variation in thecontacting state of connection part was also not seen at all, andexcellent reinforcement was achieved.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A reinforced connecting part of electroniccircuit members comprising:a high-density fine-pattern electrode; aflexible printed circuit; and a reinforcing fastener comprising asubstantially cylindrical section shaped element having edges definingan axial slit clamping said circuit members, wherein said reinforcingfastener is formed of an alloy having both superelastic and shape memorycharacteristics at a temperature above the Martensite transformationtemperature of the alloy, said alloy being brought to a temperatureabove the Martinsite transformation temperature after said slit isopened at a temperature below the martensite temperature of the alloyand the electronic circuit members are attached via said slit, wherebythe circuit members can be fastened with a substantially constant forceover time due to the superelastic and shape memory characteristics ofthe alloy.
 2. The reinforced connecting part of claim 1, including achemical connector clamped by said reinforcing fastener.
 3. A method ofconstructing a reinforced connection of electronic circuit members,comprising the steps of:positioning a connection part in acorrespondingly sized axial slit defined by edges of a substantiallycylindrical section shaped element formed of an alloy having bothsuperelastic and shaped memory properties, the alloy being below theMartinsite transformation start temperature thereof, the slit being ofsuch a size that the alloy is superelastically deformed to a pointbeyond its elastic limit when said slit is maintained at said size withthe alloy above the Martinsite transformation temperature; and causing atemperature of said alloy to rise above the Martensite transformationtemperature, whereby said connection part is held by said element in asuperelastically deformed state so that a substantially constantclamping force over time can be maintained.